In recent years, a radio communication system such as a mobile phone system or a wireless Local Area Network (LAN) has been widely used. A radio communication apparatus such as a mobile phone using a radio communication service searches a surrounding radio access network, for example, when a power supply thereof is turned on. Then the radio communication apparatus is connected to a radio access network, detected by the search, to perform voice communication and data communication.
Most of the above-described radio communication apparatuses are provided with an internal clock. A time indicated by the internal clock may be used for various purposes. For example, the time is used to display a current time on a display provided in the radio communication apparatus. Furthermore, the time may be used for Digital Rights Management (DRM). That is, when voice data or image data acquired by the data communication is reproduced, presence/absence of reproduction authority may be confirmed by referring to the current time.
Accordingly, it is preferred that the time indicated by the internal clock is correct. On the other hand, depending on a use situation of the radio communication apparatus, a deviation may be occurred between the time of the internal clock and the actual current time. For example, if the internal clock is less accurate, the deviation gradually becomes larger. If a user with the radio communication apparatus travels for a long distance, the time of the internal clock may be deviated from the destination local time because of the time difference.
To solve the above-described problem, there is a method that is to be executed by a radio communication apparatus for correcting the time of the internal clock by acquiring time information from the radio access network. For example, there is a system in which a mobile terminal requests a base station to transmit time information and the base station transmits the time information in response to the request from the mobile terminal (see, for example, Japanese Laid-open patent publication No. 2002-156478). Furthermore, there is a technique in which, in a region in which an Advanced Mobil Phone Service (AMPC) system that does not broadcast the time information and a Code Division Multiple Access (CDMA) system broadcasts the time information exist together, a mobile phone terminal device adds the CDMA system to receive the time information and then switches the connection destination to the AMPC system (see, for example, Japanese Laid-open patent publication No. 11-136755).
As described above, there are two types of radio access networks: one radio access network provides the time information and the other radio access network does not provide the time information. Accordingly, the technique described in Japanese Laid-open patent publication No. 2002-156478 is unable to correct the time in a case of using the radio access network that does not provide the time information.
As for the radio access networks with the same communication method, some radio access networks provide the time information and some radio access networks do not provide the time information. For example, in Wideband CDMA (W-CDMA), a system that provides the time information and the other system that does not provide the time information are mixed. Therefore, even the technique described in Japanese Laid-open patent publication No. 11-136755, may fail to perform time correction.